Third of a five-part series looking at the Celtics before the start of training camp Saturday.

The end of his five-year stay with the Celtics came late on a Friday night in July.

Ray Allen, unhappy with his situation in Boston, decided it was time to move on, so he signed with the defending NBA champion Miami Heat for less money.

Now 37 years old, Allen will be coming off the bench and should have plenty of open shots when LeBron James and Dwyane Wade are getting extra attention.

Allen left the Celtics, where he won a championship in 2008 and set the NBA record for career 3-pointers in 2011, because of a variety of factors.

Avery Bradley took over his starting role after Allen struggled with an ankle injury from early March through the playoffs. Allen had a diminished role in the offense, and he was not exactly on friendly terms with point guard Rajon Rondo.

It all added up to Allen moving in a different direction.

The Celtics, meanwhile, acquired a pair of shooting guards during the summer to go along with Bradley. The hope is that the defense of Bradley and the scoring capabilities of Jason Terry and Courtney Lee off the bench will fill the void left by Allen.

He was a major part of the Celtics’ five-year run, but Allen clearly struggled with the ankle injury last season. The Celtics went 16-4 in the games that he was sidelined.

The resurgence of the Celtics after the All-Star break last season was helped in large part by increased playing time for Bradley.

After rarely getting off the bench as a rookie in 2010-11 and having a slow start to the 2011-12 season, Bradley was superb when paired with Rondo in the backcourt.

He emerged as one of the leading defenders at the guard position, constantly harassing opponents from one end of the floor to the other. That helped make the Celtics a better defensive team, taking time off the 24-second clock.

Bradley’s season came to an end in the second round of the playoffs, though, because of a shoulder injury. He underwent operations on both shoulders and is not expected to be ready to play until early December.

Coach Doc Rivers has said that Lee, acquired from the Houston Rockets in a sign-and-trade move, will likely be the starter early in place of Bradley.

Page 2 of 2 - Lee will be playing for his fourth team in five seasons. He signed a four-year, $21 million contract with the Celtics, who moved E’Twaun Moore, JaJuan Johnson, Sasha Pavlovic, Sean Williams and three second-round picks to obtain Lee in a three-team swap that also involved the Portland Trail Blazers.

A first-round pick by the Orlando Magic in 2008, Lee has averaged 10 points in 287 games, making 39 percent of his 3-pointers.

The 35-year-old Terry left the Dallas Mavericks to sign with the Celtics. Unlike Allen, Terry embraces coming off the bench where he will give the Celtics a much needed boost in the area of scoring.

Terry averaged 15.1 points last season, though his shooting percentage of .430 was his lowest since the 2003-04 season.

“I’m just excited about being part of this Celtics organization, the franchise, the heritage, the tradition,’’ said Terry this summer. “I knew I was going to be a free agent and watcing the playoffs and knowing they were just one game away (from the NBA Finals), I automatically in my mind envisioned myself in a Celtics’ uniform.’’

Tomorrow: Will Rajon Rondo be even better with more fast-break options?